In certain environments, cable assemblies are stressed by dynamic loads. More particularly, in the field of remote operated vehicles (land, sea, air or space), signal transmission cable assemblies are employed to link a control system to one or more remote operated vehicles. During the employment of a remote operated vehicle and control system, dynamic loads caused by operational and environmental conditions cause the signal transmission cable assemblies to fatigue and fail. In an attempt to increase the useful life of such signal transmission cable assemblies, strength members have been incorporated into their design.
Known strength members which have been used in transmission cable design often comprise overlapping or non-parallel filaments, such as aramid fibers for example. Such non-parallel or overlapping filaments define contact points between individual filaments and other cable elements. Typically, abrasion and load concentration have occurred at such contact points, thereby reducing the tensile properties of the cable assembly. In an attempt to overcome such shortcomings regarding the use of strength members in transmission cable design, various coatings, lubricants and strength member configurations have been employed. Although such coatings, lubricants and strength member configurations have operated with varying degrees of success in certain applications, they are replete with shortcomings which have detracted from their usefulness in promoting longevity of the strength member in dynamic applications.
Lubricants have been employed to reduce friction between overlapping filaments, but such lubricants have not minimized stress concentration in tension loaded strength members. Also, during any use of lubricated strength members in a cable design, dynamic stresses and loading have displaced these lubricants from the contact points, thereby creating non-lubricated strength member regions.
Thermoplastic compression extruded coatings have been employed to reduce abrasion and load concentration at the contact points, but such coatings tend to compact the filament strength members which reduces freedom of movement of the individual filaments, increase inter-contact friction and stress concentration, and reduce the life of the strength member. Although such strength member coatings provide a substantial interface to the strength member in a longitudinal direction, such coatings provide insufficient lateral strength perpendicular to the axis of extrusion. Also, these coatings add weight and size to the strength members, which is undesirable for certain applications.
High friction coatings, such as polyurethane, have been used to enhance load sharing between strength members, however, such coatings increase internal friction of the strength member filaments, which results in degradation of the strength member during compressive loading of the strength member.
Strength member filaments have also been protected from mechanical damage by polyurethane impregnation. However, polyurethane impregnation of strength members produces a somewhat rigid strength member which increases load concentration when the strength member is subject to compression. Such a rigid strength member tends to "buckle" and "notch", which results in a point of stress concentration and strength reduction.
In addition to the foregoing, strength members have been employed in an untreated or uncoated state, and have been braided onto a cable core. However, such braiding of a strength member causes the strength member to "flatten" onto the cable core, thereby reducing load sharing characteristics between filaments and subjecting more filaments to non-parallel or overlapping interfaces. Also, uncoated or untreated fibrous strength members provide a large path for water to "wick" or migrate thereby causing electrical failure, cable weight gain, and the introduction of abrasion enhancing contaminates, such as salt crystals from marine environments. Subsequent re-termination or removal of water from the cable is laborious and costly.
The foregoing illustrates limitations known to exist in present cable assemblies. Thus, it is apparent that it would be advantageous to provide an improved cable assembly directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.